This invention relates to photographic processing apparatus, and is more particularly concerned with replenishment systems for such apparatus.
In photographic processing, the chemicals used for the development, bleaching and fixing stages need to be replenished periodically in order to produce optimum results. The rate at which the chemistry needs to be replenished depends mainly on the area and the exposure of the photographic material being processed. In known replenishment systems, replenishment is generally carried out using chemicals in liquid form and pumping volumetrically metered quantities to the appropriate stage or stages of the processing apparatus as required. Accurate metering pumps can be used to dispense the replenisher in such systems, but these tend to be very expensive. A cheaper alternative to the metering pump is a bellows pump which is not very accurate, especially when only small quantities of replenishment material need to be added.
U.S. Pat. No. 4,605,297 discloses an arrangement in which a peristaltic pump is used to dispense fluid from a bottle during the processing of photographic film material. The pump also operates to return the excess fluid from the film surface to the bottle after use. A weight sensor is used to determine the amount of fluid in the bottle. The weight sensor is not used to meter fluid from the bottle but only to determine if there is sufficient fluid in the bottle for a processing operation before it is started. However, this type of arrangement tends to be inaccurate as there is no allowance made for any fluid which is retained in pipework connecting the bottle to its dispensing station.
Another problem associated with pump-based replenishment systems is that air can be trapped in the system causing air locks. As a consequence, when a certain volume is pumped through the system to effect replenishment, there is no allowance for trapped air and less replenisher material is dispensed than desired.
It has been proposed to use a weighing system for dispensing replenishment materials. However, due to the size of the container in which the replenishment materials are stored, very expensive weighing systems need to be used to be able to dispense replenishment materials to the desired accuracy.